There has conventionally been known a movement assistance device configured to be attached to the legs of a person (human being) to be assisted and to generate power to assist the bending and stretching of his or her legs. For example, Japanese Patent Application Laid-Open No. 2014-508010 (hereinafter referred to as “Patent Literature 1”) discloses a movement assistance device which has a thigh frame and a lower leg frame to be attached to the thigh and the lower leg, respectively, of each leg of the person to be assisted, and a spring. The movement assistance device is configured to apply power to a joint mechanism between the thigh frame and the lower leg frame by the elastic force of the spring, thereby assisting the movement of the leg.